Hydroisomerization of olefin



United States Patent 3,177 ,159 HYDROISQMERIZATION 0F QLEFEN Thomas A. Rodgers, La Porte, and Maxwell Nager, Pasadena, Tex., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 27, 1961, Ser. No. 162,6il1 3 Claims. (Cl. 252-439) This invention relates to a process for the catalytic conversion of unbranched or lightly branched hydrocarbons into branched or more highly branched hydrocarbons having the same number of carbon atoms. More particularly, the process relates to the isomerization of normal olefins to isoparaflins having the same number of carbon atoms. The invention more particlularly relates to the application of a special catalyst for carrying out the isomerization.

Normal olefins in the gasoline boiling range have a high octane rating, particularly blending octane rating. However, their presence in motor gasoline in recent years has been increasingly undesirable because of their high sensitivity. By sensitivity it is meant the difierence in octane rating determined by the Research Method (F-l) and the octane rating determined according to the Motor Method (F-2).

It is known that olefins can be converted to the corresponding saturated hydrocarbons by hydrogenation, usually by a catalytic process employing a catalyst comprising a hydrogenation component on an inert support, such as the conventional cobalt molybdenum on alumina catalyst. However, while the Research octane rating of normal olefins is relatively high, the Research octane rating of the normal paraifin product obtained by simple hydrogenation is often very much lower. Therefore, simple hydrogenation processes have not been looked upon with favor since the refiner can rarely tolerate the loss in Research octane rating.

It has been proposed to hydroisomerize olefins by means of a dual function catalyst comprising a hydrogenation component associated with an acid-acting support. In

such a process, normal olefins are converted at an elevated temperature and pressure into isoparaffins. Isoparaffins have a considerably higher octane rating than the corresponding normal parafiins, thus, the hydroisomerization product is not only of the desired degree of saturation, but owing to the increase in isoparafiin content, is of a higher research octane rating than the product obtained by a conventional simple hydrogenation process. Further details of the hydroisomerization of olefins are disclosed and described in copending applica tion Serial No. 39,818, filed June 30, 1960, now Patent No. 3,149,180, by Joost C. Platteeuw and Johannes H. Choufoer.

The mechanism by which normal olefins are converted into isoparafi'ins in the presence of a dual function catalyst is not fully understood, although the simplest explanation is that the olefins are first isomerized to an isoolefin which is then hydrogenated to the corresponding isoparafiin. That the isomerization reaction proceeds before the hydrogenation reaction is supported by the observation that normal parafiins are substantially unaffected by the catalyst at the conversion conditions.

For the commercial practice of a catalytic hydroisomerization process, the catalyst should be selective and stable, i.e., the catalyst should have the ability to convert "ice the non-highly branched olefins into highly branched parafiins for an extended period of time. It isgenerally considered that selectivity is a measure of the ability of the catalyst to provide ahigh ratio of highly branched hydrocarbons to unbranched or lightly branched hydrocarbons whereas stability is a measure of the ability of the catalyst to convert olefins into paratfins.

A hydroisomerization.catalyst having a high selectivity is comprised of nickel sulfide on an acid-acting support such as acidic refractory oxides. For example, in the conversion of a normal olefin, e.g., hexene-l, withsuch a catalyst, the ratio of isoparafiin to normal paraffin in the product is at least 7:1. However, in use, the nickel sulfide catalyst rapidly loses its ability to convert the olefin to parafiins. Therefore, as olefins begin to appear in the product in substantial quantities, it is the practice to increase the conversion temperature to maintain the desired degree of saturation. Ultimately, however, usually after only a few hundred hours operation, a point is reached where; the conversion temperature has been raised to the maximum temperature desired for the process and it becomes necessary to interrupt the process and to reactivate or renew .the catalyst.

It is an object .of this invention to provide an improved process for the hydroisomerization of normal or lightly branched olefins to more highly branched parafi'ins. It is a particular object of this invention to provide an improved process for the hydroisomerization of olefins by means of a special catalyst which is selective and yet highly stable. I

It has now been found that stability of nickel sulfide hydroisomerization catalyst is greatly improved by incorporating a critically small amount of tungsten in the catalyst. Thus, the addition of tungsten to the nickel sulfide catalyst permits the hydroisomerization process to be carried out for a much longer period of time than that which is obtained with the nickel sulfide catalyst without tungsten.

The amount of nickel in the hydroisomerization catalyst can vary within wide limits and generally is in the range of from about 0.5 to about 20% by weight based on the total catalyst. For a particularly active catalyst, the amount of nickel is preferably in the range from about 6 to about 12% by weight based on the total catalyst.

The atomic ratio of nickel to tungsten in the catalyst should be greater than 10:1 and preferably greater than 15:1. With a catalyst containing higher proportion of tungsten, that is at a nickel to tungsten atomic ratio of less than 10:1 the selectivity, although high initially, levels out after a few hours at a level which is about the same as that obtained with a conventional hydrogenation catalyst such as cobalt molybdenum on alumina. On the-other hand, to obtain the benefits of the invention to an appreciable degree, the nickel to tungsten ratio should be not more than about 150:1 and preferably no more than about 125:1. A particularly preferred range for the nickelztungsten atomic ratio is about 20:1 to :1.

The tungsten and nickel components of the catalyst are intimately combined with an acid-acting catalyst such as the acid-acting refractory oxides. By an acid-acting catalyst it is meant those which when absorbing butter yellow and still other Weaker basic indicators, show a color change of these indicators, indicating the transition to the acid form. "Suitable acid-acting catalyst for the dual function hydroisomerization catalyst of the invention are compounds of silica and alumina such as silica-alumina cracking catalyst, compounds of silica and zirconium dioxide, compounds of boron trioxide and alumina, comacting catalyst, for instance silica-alumina cracking catalyst, by any suitable method known per se. For example, the tungsten and nickel can be applied byimpregnating the acid catalyst with a solution of a salt of the corresponding metal, for example, nickel nitrate and silicotungstic acid, which is then followed by drying and calcining.

The tungsten and nickel are converted at least in part to the sulfide form before use in the hydroisomerization process. The catalyst can be sulfided before placement in the reaction vessel or it can be sulfided in situ within the reactor vessel- The sulfiding can bevcarried out by any manner conventionally known in the art, such as by contacting the catalyst with a mixture of hydrogensulfide and hydrogen or by contacting the catalyst at a low temperature with a hydrocarbon containing a small amount of decomposable sulfur compound such as about 1-3%' by volume carbon disulfide.

Theprocess of the invention isparticularly suitable for the conversion of unbranched or lightly branched olefins boiling within the gasoline boiling range into more highly branched parafiins. The process is especially suitable for the conversion of unbranched or'lightly branched olefins having from 4 to 8 carbon atoms per molecule into more highly. branched paraflinic hydrocarbons. .The olefinic starting material can be one or more olefins or can be a mixture of one or more olefins andother hydrocarbons. The olefinic starting material to be converted is generally passed over the dual function catalyst at a liquid hourly space velocity of from about 0.5 to about barrels of liquid hydrocarbons per hour per. barrel of catalyst, although lower orhigher space velocities may also be used.

The conversion of olefinsin the present process is carried out in the presence ofhydrogen and at an elevated pressure, preferably at a total pressure not exceeding v1500 pounds per square inch, and'in particular at a total pressure from about 150 to about 1500 pounds per square "inch. The 'hydrogen-partial pressure may varywithin naphtha.- The sulfiding temperature was raised from approximately 270 F. to'the desired hydroisomerization wide limits and is preferably from about 50% to aboutv 95% of the total pressure. Purehydrogen is not necessarily used, as hydrogen containing gases, such "as the hydrogen rich'gases from a reforming process, are also suitable.

Conversion of the olefin is carried outat an elevated temperature generally in the range of from 400 to 900 F. and preferably 500". to 750 F.

The following examples further illustrate the process of the invention and its advantages.

EXAMPLE I A series of catalytic compounds comprising silica- .alumina, nickel sulfide and tungsten sulfide were prepared in the following manner. A commercially available -silica-alumina cracking' catalyst containing approximately 25% alumina and 75% silica was employed as the acid-acting support. The silica-alumina, in the form of pellets, was impregnated with an aqueous solution of nickel nitrate .andsilicotungstic acid, the strength of the nickel nitrate solution being selected to provide approximately 6.5% by weight nickel based on the totalcatalyst.

Total volume of impregnating 4 7 solution used was about 0.9 cc. per gram-of silicaalumina. The wetted pellets were allowed to stand for approximately 16 to 20 hours, and were then dried with stirring, under. a heat lamp. The, catalyst was then dried for an additional 3 hours at 266 F. in a vacuum. The

dried catalyst was calcined at 482 F. for 20.,hours and then calcined for an additional 5 hours at 860-F.

For comparison, another catalyst was prepared in a similar manner, but Without the additionof tungsten. This catalyst contained 9.9% nickel, based on the weight of the'total catalyst.

Prior to use, the catalysts weresulfided in the reaction vessel, using 3% by volume carbon disulfide in light temperature at the rate of about 55 F. per hour.

A'total of five nickel catalyst composites were prepared. Catalysts A, B, C, and D contained 0.25%, 1.0%, 2.5% and 10.0% by weight tungsten, respectively, which provided a nickel to tungsten atomic ratio of 81.5, 20.4; 8.2, and 2.0, respectively. Catalyst E contained 9.9% by'weight nickel and no tungsten. The five catalysts wereindividually employed in the hydroisomerization of a wide boilingrange (120-365 F.) hydrocarbon fraction comprising on a volume basis approximately 75% cracked gasoline and 25% straightrun naphtha. Properties of the hydrocarbon fraction are given in Table I.

Table-l PROPERTIES OF HYDROISOMERIZATIONVFEED API gravity at F. 54.8 Group hydrocarbon type percent v. FIA:

Saturates and naphthenes -1 38 Olefins 36 Aromatics 26 Bromine No. 57 Maleic anhydride value i 4.1 Nitrogen, p.p.m. 35 Sulfur, p.p.m. 310 Molecular weight 106 ASTM Dist, F.:

IBP I 120 5% 154 10% 173 30% 216 50% 254 288 329 350 EP 365 The hydroisomerization reaction was carried out at 750 5 lar catalyst for the hydroisomerization reaction.

The addition of tungsten tothe nickel catalyst improved stability greatly, as indicated by a run life of about 735 and 1125 hours obtained for catalysts A and B, respectively, compared with a run life of only 650 hours obtained'for catalyst E,-which contained no tungsten.

Afteran initial sharp decline, selectivity of the tungstem-containing catalysts remained substantially-constant for the remainder of the run period. With. catalyst E, which contained no tungsten, selectivity declined gradu ally throughout most of the run period.

Thus, at the end of 200 hours, whenthe selectivity had become substantially stabilized, selectivity for catalysts A through E was 6.0, 3.5, 2.3, 2.3, and 6.8, respectively. The selectivity of 2.3 for catalysts C and D was substantially the same as that obtained with a'conventional cobalt molybdenum hydrogenationcatalyst under the same conditions. Thus, the amount of tungsten added to the nickel catalyst should be kept relatively low so as to obtain the advantages of the hydroisomerization conversion.

We claim as our invention:

1. A catalyst which comprises nickel and tungsten deposited on an acid-actingsupport, the atomic ratio of nickel to tungsten being from about 10 to 1 to about 150 to 1, the amount of nickel being from about 0.5 to about 20% by weight, based on the total catalyst, and said nickel and tungsten being in the form of a sulfide.

2. A catalyst which comprises nickel and tungsten deposited on an acid-acting refractory mode support, the atomic ratio of nickel to tungsten being from about 10 to 1 to about 150 to 1, the amount of nickel being from about 0.5 to about 20% by weight, based on the total catalyst, and said nickel and tungsten being in the form of a sulfide,

3. A catalyst which comprises nickel and tungsten deposited on silica-alumina, the atomic ratio of nickel to tungsten being from about 10 to 1 to about 150 to 1, the amount of nickel being from about 0.5 to about 20% by weight, based on the total catalyst, and said nickel and tungsten being in the form of a sulfide.

References Cited by the Examiner UNITED STATES PATENTS ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A CATALYST WHICH COMPRISES NICKEL AND TUNGSTEN DEPOSITED ON AN ACID-ACTING SUPPORT, THE ATOMIC RATIO OF NICKEL TO TUNGSTEN BEING FROM ABOUT 10 TO 1 TO ABOUT 150 TO 1, THE AMOUNT OF NICKEL BEING FROM ABOUT 0.5 TO ABOUT 20% BY WEIGHT, BASED ON THE TOTAL CATALYST, AND SAID NICKEL AND TUNGSTEN BEING IN THE FORM OF A SULFIDE. 